Inter-cervical facet implant with multiple direction articulation joint and method for implanting

ABSTRACT

Systems and method in accordance with the embodiments of the present invention can include an implant for positioning within a cervical facet joint for distracting the cervical spine, thereby increasing the area of the canals and openings through which the spinal cord and nerves must pass, and decreasing pressure on the spinal cord and/or nerve roots. The implant can be inserted laterally or posteriorly.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Application No.60/687,765, entitled “Inter-Cervical Facet Implant With MultipleDirection Articulation Joint And Method For Implanting,” filed Jun. 6,2005, which is incorporated herein by reference in its entirety.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. Provisional Patent Application incorporates by reference allof the following co-pending applications and issued patents:

U.S. Provisional Application No. 60/635,435, entitled “Inter-CervicalFacet Implant and Method,” filed Dec. 13, 2004;

U.S. application Ser. No. 11/053,399, entitled “Inter-Cervical FacetImplant and Method,” filed Feb. 8, 2005;

U.S. application Ser. No. 11/053,624, entitled “Inter-Cervical FacetImplant and Method,” filed Feb. 8, 2005;

U.S. application Ser. No. 11/053,735, entitled “Inter-Cervical FacetImplant and Method,” filed Feb. 8, 2005;

U.S. application Ser. No. 11/093,557, entitled “Inter-Cervical FacetImplant with Locking Screw and Method,” filed Mar. 30, 2005;

U.S. Provisional Application No. 60/679,363, entitled “Inter-CervicalFacet Implant with Implantation Tool,” filed May 10, 2005;

U.S. Provisional Application No. 60/679,361, entitled “Inter-CervicalFacet Implant with Implantation Tool,” filed May 10, 2005;

U.S. Provisional Application No. 60/679,377, entitled “Inter-CervicalFacet Implant with Implantation Tool,” filed May 10, 2005;

U.S. application Ser. No. 11/429,905, entitled “Inter-Cervical FacetImplant with Implantation Tool,” filed May 8, 2006;

U.S. application Ser. No. 11/429,726, entitled “Inter-Cervical FacetImplant with Implantation Tool,” filed May 8, 2006;

U.S. application Ser. No. 11/429,733, entitled “Inter-Cervical FacetImplant with Implantation Tool,” filed May 8, 2006;

International Patent Application No. PCT/US2005/044979, entitled“Inter-Facet Implant,” filed Dec. 13, 2005;

U.S. application Ser. No. 11/053,346, entitled “Inter-Cervical FacetImplant and Method,” filed Feb. 8, 2005;

U.S. application Ser. No. 11/093,689, entitled “Inter-Cervical FacetImplant and Method for Preserving the Tissues Surrounding the FacetJoint,” filed Mar. 30, 2005;

U.S. Provisional Application No. 60/668,053, entitled “Inter-CervicalFacet Implant Distraction Tool,” filed Apr. 4, 2005; and

U.S. application Ser. No. 11/397,220, entitled “Inter-Cervical FacetImplant Distraction Tool, filed Apr. 4, 2005.

TECHNICAL FIELD

This invention relates to interspinous process implants.

BACKGROUND OF THE INVENTION

The spinal column is a bio-mechanical structure composed primarily ofligaments, muscles, vertebrae and intervertebral disks. Thebio-mechanical functions of the spine include: (1) support of the body,which involves the transfer of the weight and the bending movements ofthe head, trunk and arms to the pelvis and legs, (2) complexphysiological motion between these parts, and (3) protection of thespinal cord and the nerve roots.

As the present society ages, it is anticipated that there will be anincrease in adverse spinal conditions which are characteristic of olderpeople. By way of example only, with aging comes an increase in spinalstenosis (including, but not limited to, central canal and lateralstenosis), and facet arthropathy. Spinal stenosis results in a reductionforaminal area (i.e., the available space for the passage of nerves andblood vessels) which compresses the cervical nerve roots and causesradicular pain. Humpreys, S. C. et al., Flexion and traction effect onC5-C6foraminal space, Arch. Phys. Med. Rehabil., vol. 79 at 1105(September 1998). Another symptom of spinal stenosis is myelopathy,which results in neck pain and muscle weakness. Id. Extension andipsilateral rotation of the neck further reduces the foraminal area andcontributes to pain, nerve root compression, and neural injury. Id.;Yoo, J. U. et al., Effect of cervical spine motion on the neuroforaminaldimensions of human cervical spine, Spine, vol. 17 at 1131 (Nov. 10,1992). In contrast, neck flexion increases the foraminal area. Humpreys,S. C. et al., supra, at 1105.

In particular, cervical radiculopathy secondary to disc herniation andcervical spondylotic foraminal stenosis typically affects patients intheir fourth and fifth decade, and has an annual incidence rate of 83.2per 100,000 people (based on 1994 information). Cervical radiculopathyis typically treated surgically with either an anterior cervicaldiscectomy and fusion (“ACDF”) or posterior laminoforaminotomy (“PLD”),with or without facetectomy. ACDF is the most commonly performedsurgical procedure for cervical radiculopathy, as it has been shown toincrease significantly the foramina dimensions when compared to a PLF.

It is desirable to eliminate the need for major surgery for allindividuals, and in particular, for the elderly. Accordingly, a needexists to develop spine implants that alleviate pain caused by spinalstenosis and other such conditions caused by damage to, or degenerationof, the cervical spine.

The present invention addresses this need with implants and methods forimplanting an apparatus into at least one facet joint of the cervicalspine to distract the cervical spine while preferably preservingmobility and normal lordotic curvature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral view of two adjacent cervical vertebrae andspinous processes, highlighting the cervical facet joint.

FIG. 2 depicts a lateral view of the cervical spine with spinalstenosis.

FIG. 3A depicts correction of cervical stenosis or other ailment with awedge-shaped embodiment of the implant of the invention positioned inthe cervical facet joint.

FIG. 3B depicts correction of cervical kyphosis or loss of lordosis witha wedge-shaped embodiment of the invention with the wedge positioned inthe opposite direction as that depicted in FIG. 3A.

FIG. 4 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention including a screwfixation device for attaching to a single vertebra.

FIG. 5 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising screwfixation of two implants, one implant fixed to each of two adjacentvertebrae.

FIG. 6 shows cervical spine kyphosis, or loss of lordosis.

FIG. 7 shows correction of cervical kyphosis, or loss of lordosis, witha further embodiment of the implant of the invention comprising twofacet implants with screw fixation.

FIG. 8 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant and a keel.

FIG. 9 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising facetimplant, a keel, and screw fixation.

FIG. 10 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant with teeth.

FIG. 11 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant with teeth and screw fixation.

FIG. 12 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces.

FIG. 13 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces and posterior alignment guide.

FIG. 14 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants with increased facet joint contact surfaces.

FIG. 15 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces and screw fixation.

FIG. 16 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants with articular inner surfaces.

FIG. 17 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetjoint implant with a roller.

FIG. 18 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetjoint implant with a plurality of rollers.

FIG. 19 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and elastic restraint.

FIG. 20 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and spring restraint.

FIG. 21 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and magnetic restraint.

FIG. 22A shows a perspective view of a further embodiment of implant ofthe invention.

FIG. 22B shows a perspective exploded view of the embodiment of theinvention shown in FIG. 22A.

FIG. 23A depicts a posterior view of the embodiment of the implant ofthe invention shown in FIG. 22A.

FIG. 23B shows a posterior view of a locking plate of the embodiment ofthe implant of the invention shown in FIG. 22A.

FIG. 24A depicts a lateral side view of the embodiment of the implant ofthe invention shown in FIG. 22A.

FIG. 24B shows a lateral side view of the keel of the locking plate ofthe embodiment of the implant of the invention shown in FIG. 22A.

FIG. 25A shows a perspective view of a further embodiment of the implantof the invention.

FIG. 25B shows a side view of the embodiment of the implant of theinvention in FIG. 25A, having a curved, uniformly-thick artificial facetjoint spacer or inter-facet spacer including a tapered end

FIG. 26A shows a perspective view of a further embodiment of the implantof the invention having a locking cam in a first position.

FIG. 26B shows a perspective view of a further embodiment of the implantof the invention having a locking cam in a second position.

FIG. 27A depicts a side view of the embodiment of the implant of theinvention shown in FIGS. 26A and 26B, implanted in a cervical spine.

FIG. 27B shows a posterior perspective view of the embodiment of theimplant of the invention depicted in FIGS. 26A, 26B and FIG. 27A.

FIG. 28A depicts a posterior perspective view of a further embodiment ofthe implant of the invention.

FIG. 28B depicts a side view of the embodiment of the implant of theinvention shown in FIG. 28A.

FIG. 29A depicts a side view of an embodiment of a sizing tool of theinvention.

FIG. 29B depicts a top view of an embodiment of the sizing tool of theinvention depicted in FIG. 29A.

FIG. 29C depicts a perspective view of an embodiment of the sizing toolof the invention depicted in FIGS. 29A and 29B.

FIG. 29D depicts a side view of the head of the sizing tool of theinvention depicted in FIG. 29A.

FIG. 29E depicts a cross-sectional view of the head of the sizing toolof the invention depicted in FIGS. 29A-29C.

FIG. 30 is a flow diagram of an embodiment of a method of the invention.

FIG. 31A is posterior view of a further embodiment of the implant of theinvention.

FIG. 31B is a side view of an embodiment of a locking screw of theimplant of the invention depicted in FIG. 31A.

FIG. 32 is a posterior view of a further embodiment of the implant ofthe invention.

FIGS. 33A and 33B depict initial and final insertion positions of theembodiment of the invention depicted in FIG. 32.

FIGS. 34A and 34B illustrate a top and bottom plan view of analternative embodiment of an inter-cervical facet implant in accordancewith the present invention.

FIG. 35 is a partially exploded perspective view of the implant of FIGS.34A and 34B.

FIGS. 36A and 36B illustrate side views of the implant of FIGS. 34A and34B illustrating a general range of motion of the implant.

FIG. 37 is a side view of still another embodiment of an implant inaccordance with the present invention.

FIG. 38 is a flow diagram of an alternative embodiment of a method inaccordance with the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide for a minimally invasivesurgical implantation method and apparatus for cervical spine implantsthat preserves the physiology of the spine. In particular, embodimentsprovide for distracting the cervical spine to increase the foraminaldimension in extension and neutral positions. Such implants, whenimplanted in the cervical facet joints, distract, or increase the spacebetween, the vertebrae to increase the foraminal area or dimension, andreduce pressure on the nerves and blood vessels of the cervical spine.

The facet joints in the spine are formed between two vertebrae asfollows. Each vertebra has four posterior articulating surfaces: twosuperior facets and two inferior facets, with a superior facet from alower vertebra and an inferior facet of an upper vertebra forming afacet joint on each lateral side of the spine. In the cervical spine,the upward inclination of the superior articular surfaces of the facetjoints allows for considerable flexion and extension, as well as forlateral mobility. Each facet joint is covered by a dense, elasticarticular capsule, which is attached just beyond the margins of thearticular facets. The capsule is larger and looser in the cervical spinethan in the thoracic and lumbar spine. The inside of the capsule islined by a synovial membrane which secretes synovial fluid forlubricating the facet joint. The exterior of the joint capsule issurrounded by a capsular ligament. It is this ligament and the jointcapsule that must be cut in the embodiments of the method describedherein for inserting the artificial facet joint.

In a specific preferred embodiment, an implanted interfacet spacer of1.5 mm to 2.5 mm in width can result in interfacet distraction thatincreases foraminal dimension in extension and neutral. Other interfacetspacer dimensions also are contemplated by the invention describedherein below. The present embodiments also preserve mobility of thefacet joints.

Further embodiments of the present invention accommodate the distinctanatomical structures of the spine, minimize further trauma to thespine, and obviate the need for invasive methods of surgicalimplantation. Embodiments of the present invention also address spinalconditions that are exacerbated by spinal extension.

FIG. 1 shows a simplified diagram of a portion of the cervical spine,focusing on a cervical facet joint 1 formed between two adjacentcervical vertebrae. The spinous processes 3 are located posteriorly andthe vertebral bodies 5 are located anteriorly, and a nerve root canal 7is visible. Each vertebra has four posterior articulating surfaces: twosuperior facets and two inferior facets, with a superior facet from alower vertebra and an inferior facet of an upper vertebra forming afacet joint on each lateral side of the spine. In the cervical spine,the upward inclination of the superior articular surfaces of the facetjoints allows for considerable flexion and extension, as well as forlateral mobility. Each facet joint is covered by a dense, elasticarticular capsule, which is attached just beyond the margins of thearticular facets. The capsule is large and looser in the cervical spinethan in the thoracic and lumbar spine. The inside of the capsule islined by a synovial membrane which secretes synovial fluid forlubricating the facet joint. The exterior of the joint capsule issurrounded by a capsular ligament. It is this ligament that may bepushed out of the way in the embodiments of the method for inserting thefacet joint spacer or inter-facet spacer, described herein.

FIG. 2 depicts cervical foraminal stenosis. From the drawing, the nerveroot canal 7 is narrowed relative to the nerve root canal 7 depicted inFIG. 1. The spinal canal and/or intervertebral foramina also can benarrowed by stenosis. The narrowing can cause compression of the spinalcord and nerve roots.

FIG. 3A shows a first embodiment 100 of the present invention, which ismeant to distract at least one facet joint, in order to increase thedimension of the neural foramen while retaining facet joint mobility.The wedge-shaped embodiment 100 is a wedge-shaped implant that can bepositioned in the cervical facet joint 101 to distract the joint andreverse narrowing of the nerve root canal 107. In this embodiment 100,the implant is positioned with the narrow portion of the wedge facinganteriorly. However, it is also within the scope of the presentinvention to position embodiment 100 (FIG. 3B) with the wide portion ofthe wedge facing anteriorly, to correct for cervical kyphosis or loss ofcervical lordosis.

Referring to FIG. 4, the embodiment 200 of the implant has a jointinsert or inter-facet spacer 210, also herein referred to as a facetjoint spacer or inter-facet spacer, that is positioned in the cervicalfacet joint 101. The joint insert or inter-facet spacer 210 can bewedge-shaped with the narrow part of the wedge facing anteriorly.Alternatively, the joint insert or inter-facet spacer 210 need not bewedge-shaped but can be of substantially uniform thickness, thethickness determined by an individual patient's need for distraction ofthe cervical facet joint 201. As with embodiment 100, one objective ofthis embodiment is facet joint distraction, and joint mobility afterimplantation. The joint insert or inter-facet spacer 210 is continuouswith a posterior sheath 220 bent at an angle from the joint insert orinter-facet spacer 210 to align substantially parallel with the bone.The posterior sheath can lie against the lamina, preferably against thelateral mass. The posterior sheath 220 can have a bore 230 which canaccept a bone screw 240. Alternatively, the bore 230 can accept anyother appropriate and/or equivalent fixation device capable of fixingthe embodiment 200 to the spine. The device is thereby affixed to thevertebra, preferably by fixing to the lateral mass.

FIG. 5 shows embodiment 300, which is the use of two embodiments 200,each fixed to one of two adjacent cervical vertebrae. As with embodiment200, the implanted facet joint is distracted and joint mobility isretained. A joint insert or inter-facet spacer 310 from each of the twoimplants is inserted and positioned in the cervical facet joint 301. Inthis embodiment, the joint inserts or inter-facet spacers 310 aresubstantially flat and parallel to each other and are not wedge-shaped.Attentively, the joint inserts or inter-facet spacers 310 can togetherdefine a wedge-shaped insert that is appropriate for the patient. Thetwo joint inserts or inter-facet spacers 310 combined can have, by wayof example, the shape of the joint insert or inter-facet spacer 210 inFIG. 4. Embodiment 300 then can be fixed to the spine with a screw 340or any other appropriate fixation device, inserted through a bore 330 inthe posterior sheath 320. The posterior sheath 320 can be threaded toaccept a screw. The screw can be embedded in the lamina, preferably inthe lateral mass, where possible.

It is within the scope of the present invention to use and/or modify theimplants of the invention to correct cervical spine kyphosis, or loss oflordosis. FIG. 6 depicts a cervical spine lordosis. FIG. 7 demonstratesan embodiment 400 which contemplates positioning two implants to correctfor this spinal abnormality while retaining facet joint mobility. Thejoint insert or inter-facet spacer 410 of each implant is shaped so thatit is thicker at its anterior portion. Alternatively, the implants canbe shaped to be thicker at the posterior ends, for example as depictedin FIG. 3A. The posterior sheath 420 of each implant is bent at an anglefrom the joint insert or inter-facet spacer 410 to be positionedadjacent to the lateral mass and/or lamina, and has a bore 430 to accepta screw 440 or other appropriate and/or equivalent fixation means to fixthe embodiment 400 to the spine, preferably to the lateral mass. Theplacement of two joint inserts or inter-facet spacers 410 in thecervical facet joint 401 distracts the facet joint, which shifts andmaintains the vertebrae into a more anatomical position to preserve thephysiology of the spine.

FIG. 8 shows a further embodiment 500 of the implant of the invention,wherein the joint insert or inter-facet spacer 510 has a keel 550 on anunderside of the joint insert or inter-facet spacer 510. The keel 550can be made of the same material or materials set forth above. Thesurfaces of the keel 550 can be roughened in order to promote boneingrowth to stabilize and fix the implant 500. In other embodiments, thekeel 550 can be coated with materials that promote bone growth such as,for example, bone morphogenic protein (“BMP”), or structural materialssuch as hyaluronic acid “HA,” or other substances which promote growthof bone relative to and into the keel 550.

The keel 550 can be embedded in the facet bone, to facilitate implantretention. The keel 550 can be placed into a channel in the facet bone.The channel can be pre-cut. Teeth (not shown), preferably positionedposteriorly, also may be formed on the keel 550 for facilitatingretention of the implant 500 in the cervical facet joint 501. As notedabove, the joint insert or inter-facet spacer 510 can be substantiallyflat or wedge-shaped, depending upon the type of distraction needed,i.e., whether distraction is also necessary to correct abnormalcurvature or lack of curvature in the cervical spine. Because the jointis not fused, mobility is retained, as with the embodiments describedabove and herein below.

FIG. 9 illustrates that a further embodiment 600 of the implant of theinvention can have both screw fixation and a keel 650 for stability andretention of the implant 600. On embodiment 600, the joint insert orinter-facet spacer 610 is continuous with a posterior sheath 620 havinga bore hole 630 to accept a screw 640 which passes through the bore 630and into the bone of the vertebrae, preferably into the lateral mass, orthe lamina. The bore 630 can be threaded or not threaded where it is toaccept a threaded screw or equivalent device. Alternatively, the bore630 need not be threaded to accept a non-threaded equivalent device. Thekeel 650 is connected with the joint insert or inter-facet spacer 610and embeds in the bone of the cervical facet joint 601 to promoteimplant retention.

A further alternative embodiment 700 is illustrated in FIG. 10. In thisembodiment 700, the joint insert or inter-facet spacer 710 has on alower side at least one tooth 760. It should be clear to one of ordinaryskill in the art that a plurality of teeth 760 is preferable. The teeth760 are able to embed in the bone of the cervical facet joint 701 tofacilitate retention of the implant 700 in the joint 701. The teeth 760can face in a direction substantially opposite the direction ofinsertion, for retention of the implant 700. As above, the joint insertor inter-facet spacer 710 can be wedge-shaped or substantially even inthickness, depending upon the desired distraction. Because the implantdistracts and is retained without fusion, facet joint mobility isretained.

FIG. 11 depicts a further embodiment 800 of the implant of theinvention. In this embodiment 800, the joint insert or inter-facetspacer 810 is continuous with a posterior sheath 820 having a bore 830for accepting a fixation device 840, as described above. The fixationdevice 840 can be a screw which fits into a threaded bore 830;alternatively, the fixation device 830 can be any other compatible andappropriate device. This embodiment 800 further combines at least onetooth 860 on an underside of the joint insert or inter-facet spacer 810with the posterior sheath 820, bore 830 and fixation device 840 toaddress fixation of the implant 800 in a cervical facet joint 801. Itwill be recognized by one of ordinary skill in the art that the implant800 can have a plurality of teeth 860 on the underside of the jointinsert or inter-facet spacer 810.

FIG. 12 shows yet another embodiment 900 of an implant of the presentinvention. In this embodiment 900, the joint inserts or inter-facetspacers 910 of two implants 900 are positioned in a cervical facet joint901. As described above, the joint inserts or inter-facet spacers 910can be wedge-shaped as needed to restore anatomical curvature of thecervical spine and to distract, or the joint inserts or inter-facetspacers 910 can be of substantially uniform thickness. The implants 900each comprise a joint insert or inter-facet spacers 910 with an outersurface 970 that interacts with the bone of the cervical facet joint901. On the upper implant 900, the surface 970 that interacts with thebone is the upper surface 970 and on the lower implant 900, the surface970 that interacts with the bone is the lower surface 970. Each surface970 can comprise a bone ingrowth surface 980 to create a porous surfaceand thereby promote bone ingrowth and fixation. One such treatment canbe with plasma spray titanium, and another, with a coating of sinteredbeads. Alternatively, the implant 900 can have casted porous surfaces970, where the porous surface is integral to the implant 900. As afurther alternative, the surfaces 970 can be roughened in order topromote bone ingrowth into these defined surfaces of the implants 900.In other embodiments, the surfaces 970 can be coated with materials thatpromote bone growth such as for example bone morphogenic protein(“BMP”), or structural materials such as hyaluronic acid (“HA”), orother substances which promote growth of bone on other external surfaces970 of the implant 900. These measures facilitate fixation of theimplants 900 in the facet joint, but do not result in fusion of thejoint, thereby retaining facet joint mobility, while also accomplishingdistraction of the joint.

FIG. 13 depicts yet another embodiment 1000 of the implant of thepresent invention. In this embodiment 1000, the joint inserts orinter-facet spacers 1010 of two implants 1000 are positioned in acervical facet joint 1001. As described above, the joint inserts orinter-facet spacers 1010 can be wedge-shaped as needed to restoreanatomical curvature of the cervical spine and to distract, or the jointinserts or inter-facet spacers 1010 can be of substantially uniformthickness. The implants 1000 each comprise a joint insert or inter-facetspacer 1010 with an outer surface 1070 that interacts with the bone ofthe cervical facet joint 1001. On the upper implant 1000, the surface1070 that interacts with the bone is the upper surface and on the lowerimplant 1000, the surface 1070 that interacts with the bone is the lowersurface. As set forth above, each outer surface 1070 can comprise a boneingrowth surface 1080 to create a porous surface and thereby promotebone ingrowth and fixation, without facet joint fusion and loss ofmobility. In one preferred embodiment, the bone ingrowth surface 1080can be created with plasma spray titanium, and/or with a coating ofsintered beads. In an alternative preferred embodiment, the implant 1000can have casted porous surfaces 1070, where the porous surface isintegral to the implant 1000. In a further alternative preferredembodiment, the surfaces 1070 can be roughened in order to promote boneingrowth into these defined surfaces of the implants 1000. In otherpreferred embodiments, the surfaces 1070 can be coated with materialsthat promote bone growth such as for example BMP, or structuralmaterials such as HA, or other substances which promote growth of boneon other external surfaces 1070 of the implant 1000.

The implant 1000 can have a posterior alignment guide 1090. Theposterior alignment guides 1090 of each implant 1000 can be continuouswith the joint inserts or inter-facet spacers 1010. The posterioralignment guides substantially conform to the bone of the vertebrae whenthe joint inserts or inter-facet spacers 1010 are inserted into thecervical facet joint 1001. The posterior alignment guides 1090 are usedto align the implants 1000 so that the joint inserts or inter-facetspacers 1010 contact each other and not the bones of the cervical facetjoint 1001 when the joint inserts or inter-facet spacers 1010 arepositioned in the cervical facet joint 1001.

FIG. 14 depicts a further embodiment 1100 of the implant of the presentinvention. In this embodiment 1100, the joint inserts or inter-facetspacers 1110 of two implants 1100 are inserted into the cervical facetjoint 1101. Each of the joint inserts or inter-facet spacers 1110 iscontinuous with a cervical facet joint extender or facet-extendingsurface 1192. The bone contacting surfaces 1170 of the joint inserts orinter-facet spacers 1110 are continuous with, and at an angle to, thebone contacting surfaces 1193 of the cervical facet joint extenders1192, so that the cervical facet joint extenders 1192 conform to thebones of the vertebrae exterior to the cervical facet joint 1101. Theconformity of the cervical facet joint extenders 1192 is achieved forexample by forming the cervical facet joint extenders 1192 so that whenthe join inserts or inter-facet spacers 1110 are positioned, thecervical facet joint extenders 1192 curve around the bone outsider thecervical facet joint 1101.

The cervical facet joint extenders have a second surface 1184 that iscontinuous with the joint articular surfaces 1182 of the joint insertsor inter-facet spacers 1110. The second surfaces 1184 extend the implant1100 posteriorly to expand the joint articular surfaces 1182 and therebyto increase contact and stability of the spine at least in the region ofthe implants 1100. It is to be understood that such facet jointextenders 1192 can be added to the other embodiments of the inventiondescribed and depicted herein.

The embodiment depicted in FIG. 15 shows two implants 1200 positioned ina cervical facet joint 1201, having bony ingrowth surfaces as onepreferred method of fixation, and using screws as another preferredmethod of fixation. In this embodiment, each of two implants 1200 has ajoint insert or inter-facet spacer 1210 positioned in a cervical facetjoint 1201. As described above, the joint inserts or inter-facet spacers1210 can be wedge-shaped as needed to restore anatomical curvature ofthe cervical spine and to distract, or the joint inserts or inter-facetspacers 1210 can be of substantially uniform thickness. The implants1200 each comprise a joint insert or inter-facet spacer 1210 with anouter surface 1270 that interacts with the bone of the cervical facetjoint 1201. On the upper implant 1200, the surface 1270 that interactswith the bone is the upper surface and on the lower implant 1200, thesurface 1270 that interacts with the bone is the lower surface. As setforth above, each outer surface 1270 can comprise a bone ingrowthsurface 1280 to create a porous surface and thereby promote boneingrowth and fixation. In one preferred embodiment, the bone ingrowthsurface 1280 can be created with plasma spray titanium, and/or with acoating of sintered beads. In an alternative preferred embodiment, theimplant 1200 can have casted porous surfaces 1270, where the poroussurface is integral to the implant 1200. In a further alternativeembodiment, the surfaces 1270 can be roughened in order to promote boneingrowth into these defined surfaces of the implants 1200. In otherpreferred embodiments, the surfaces 1270 can be coated with materialsthat promote bone growth such as for example BMP, or structuralmaterials such as HA, or other substances which promote growth of boneon other external surfaces 1270 of the implant 1200.

Screw fixation or other appropriate fixation also can be used withimplants 1200 for fixation in the cervical facet joint 1201. The jointinsert or inter-facet spacer 1210 is continuous with a posterior sheath1220 bent at an angle from the joint insert or inter-facet spacer 1210to align substantially parallel with the bone, preferably the lateralmass or lamina. The posterior sheath 1220 can have a bore 1230 which canaccept a bone screw 1240, preferably into the lateral mass or lamina.Alternatively, the bore 1230 can accept any other appropriate and/orequivalent fixation means for fixing the embodiment 1200 to the spine.

FIG. 16 depicts a further preferred embodiment of the present invention.In this embodiment 1300, two joint inserts or inter-facet spacers 1310are positioned in the cervical facet joint 1301. The joint inserts orinter-facet spacers each have outer surfaces 1370 that interact with thebone of the vertebrae forming the cervical facet joint. These outersurfaces 1370 of the embodiment 1300 can be treated to become boneingrowth surfaces 1380, which bone ingrowth surfaces 1380 contribute tostabilizing the two joint inserts or inter-facet spacers 1310 of theimplant 1300. In one preferred embodiment, the bone ingrowth surface1380 can be created with plasma spray titanium, and/or with a coating ofsintered beads. In an alternative preferred embodiment, the implant 1300can have casted porous surfaces 1370, where the porous surface isintegral to the implant 1300. In a further alternative embodiment, thesurfaces 1370 can be roughened in order to promote bone ingrowth intothese defined surfaces of the implants 1300. In other preferredembodiments, the surfaces 1370 can be coated with materials that promotebone growth such as for example BMP, or structural materials such as HA,or other substances which promote growth of bone on other externalsurfaces 1370 of the implant 1300. This fixation stabilizes the implant1300 in the facet joint without fusing the joint, and thus the implantpreserves joint mobility, while accomplishing distraction and increasingforaminal dimension.

Also shown in FIG. 16 are articular inner surfaces 1382 of the implants1300. These surfaces can be formed from a metal and polyethylene, thematerial allowing flexibility and providing for forward bending/flexionand backward extension of the cervical spine. The embodiment 1300 ofFIG. 16 can be made in at least two configurations. The firstconfiguration includes a flexible spacer 1382 made, by way of example,using polyethylene or other suitable, flexible implant material. Theflexible spacer 1382 can be permanently affixed to the upper and lowerjoint insert or inter-facet spacer 1310. The spacer 1382 can be flat orwedge-shaped or have any other shape that would correct the curvature ofthe spine. In other configurations, the spacer 1382 can be affixed toonly the upper insert or inter-facet spacer 1310 or to only the lowerinsert or inter-facet spacer 1310. Alternatively, a spacer 1382 can beaffixed to each of an upper insert or inter-facet spacer 1310 and alower insert or inter-facet spacer 1310 with the upper insert orinter-facet spacer 1310 and the lower insert or inter-facet spacer 1310being separate units.

FIG. 17 shows a further preferred embodiment of the implant of thepresent invention. In this embodiment 1400, the implant has a roller1496 mounted on a joint insert or inter-facet spacer 1410, the rollerbeing a further means of preserving joint mobility while accomplishingdistraction. Both the roller 1496 and the joint insert or inter-facetspacer 1410 are positioned in the cervical facet joint 1401. The jointinsert or inter-facet spacer 1410 as in other embodiments has abone-facing surface 1470 and joint articular surface 1482. Thebone-facing surface 1470 can interact with the lower bone of thecervical facet joint 1401. Alternatively, the bone-facing surface caninteract with the upper bone of the cervical facet joint 1401. Betweenthe bone-facing surface 1470 and the joint articular surface 1482 is anaxis about which the roller 1496 can rotate. The roller 1496 rotates ina cavity in the joint insert or inter-facet spacer 1410, and interactswith the top bone of the cervical facet joint 1401. Alternatively, wherethe bone-facing surface 1470 of the joint insert or inter-facet spacer1410 interacts with the top bone of the cervical facet joint 1401, theroller 1496 rotates in a cavity in the joint insert or inter-facetspacer 1410 and interacts with the lower bone of the cervical facetjoint 1401. The rotation of the roller 1496 allows flexion and extensionof the cervical spine. Alternatively, a roller such as roller 1496 canbe secured to an upper and a lower insert such as inserts or spacers 410in FIG. 7. As depicted in FIG. 18, a plurality of rollers 1496 also ispossible.

FIG. 19 depicts a further embodiment of the implant of the presentinvention. In this embodiment, two implants 1500 are implanted in thecervical facet joint 1501. Screw fixation or other appropriate fixationis used with implants 1500 for fixation in the cervical facet joint1501. The joint insert or inter-facet spacer 1510 is continuous with aposterior sheath 1520 bent at an angle from the joint insert orinter-facet spacer 1510 to align substantially parallel with the bone,preferably the lateral mass or lamina. The posterior sheath 1520 of eachimplant 1500 can have a bore 1530 which can accept a bone screw 1540,preferably into the lateral mass or lamina. Alternatively, the bore 1530can accept any other appropriate and/or equivalent fixation means forfixing the embodiment 1500 to the spine. The head of the screw 1540 ineach posterior sheath 1520 of each implant 1500 has a groove 1598 orother mechanism for retaining an elastic band 1597. The elastic band1597 is looped around each of the two screws 1540 to restrain movementof the cervical spine without eliminating facet joint mobility. The band1597 preferably can restrain flexion and lateral movement. The elasticband 1597 can be made of a biocompatible, flexible material.

FIG. 20 shows an alternative to use of an elastic band as in FIG. 19. Inthe embodiment in FIG. 20, the elastic band is replaced with a springrestraint 1699, which extends between the heads of two screws 1640, onescrew fixing each of two implants 1600 in the cervical facet joint 1601.

FIG. 21 shows another alternative to using an elastic band and/or aspring as in FIG. 19 or 20. In FIG. 21, magnets 1795 is used forrestraint between the two screws 1740. The magnet 1795 can either becomprised of two opposing magnetic fields or two of the same magneticfields to operate to restrain movement. The head of one of the twoscrews 1740 is magnetized, and the head of the other screw 1740 ismagnetized with either the same or opposite field. If the magnets 1795have the same polarity, the magnets 1795 repel each other and thus limitextension. If the magnets 1795 have opposite polarities, the magnets1795 attract each other and thus limit flexion and lateral movement.

FIGS. 22A-24B, depict a further embodiment 1800 of the implant of thepresent invention. In this embodiment, a facet joint spacer (or insert)or inter-facet spacer (or insert) 1810 is connected with a lateral massplate (also referred to herein as an anchoring plate) 1820 with a hinge1822. The hinge 1822 allows the lateral mass plate 1820 to bend at awide range of angles relative to the facet joint spacer or inter-facetspacer and preferably at an angle of more than 90 degrees, and thisflexibility facilitates positioning and insertion of the facet jointspacer or inter-facet spacer 1810 into a patient's facet joint, theanatomy of which can be highly variable among individuals. Thischaracteristic also applies to embodiments described below, which have ahinge or which are otherwise enabled to bend by some equivalentstructure or material property. The hinge 1822 further facilitatescustomizing the anchoring of the implant, i.e., the positioning of afixation device. The hinge enables positioning of the lateral mass plate1820 to conform to a patient's cervical spinal anatomy, and the lateralmass plate 1820 accepts a fixation device to penetrate the bone. Thefacet joint spacer or inter-facet spacer 1810 can be curved or roundedat a distal end 1812 (FIG. 23A), and convex or dome-shaped on a superiorsurface 1813 to approximate the shape of the bone inside the facetjoint. The inferior surface 1815 can be flat or planar. Alternatively,the inferior surface 1815 can be concave. As another alternative, theinferior surface 1815 can be convex.

The lateral mass plate 1820, when implanted in the spine, is positionedoutside the facet joint, preferably against the lateral mass or againstthe lamina. The lateral mass plate 1820 has a bore 1830 therethrough.The bore 1830 can accept a bone screw 1840, also referred to as alateral mass screw, to secure the lateral mass plate 1820 preferably tothe lateral mass or alternatively to another part of the spine, and thusto anchor the implant. The lateral mass screw 1840 preferably has ahexagonal head to accept an appropriately-shaped wrench. As describedbelow, the head accepts a compatible probe 1826 from a locking plate1824.

The locking plate 1824 includes a keel 1828 with a wedge shaped distalend to anchor the implant, preferably in the lateral mass or in thelamina, outside the facet joint and to prevent rotation of the lateralmass plate 1820 and the locking plate 1824. The keel 1828 aligns with agroove 1823 through an edge of the lateral mass plate 1820 to guide andalign the keel 1828 as the keel 1828 cuts into a vertebra.

As noted above, the locking plate 1824 includes a probe 1826 that fitsagainst the head of the lateral mass screw 1840. The locking platefurther includes a bore 1831 that can accept a machine screw (not shown)which passes through to an aligned bore 1829 in the lateral mass plate1820 to hold the locking plate 1824 and the lateral mass plate 1820together without rotational displacement relative to each other. Thelocking plate 1824 thus serves at least two functions: (1) maintainingthe position of the lateral mass screw 1840 with the probe 1826, so thatthe screw 1840 does not back out; and (2) preventing rotation of theimplant with the keel 1828 and machine screw relative to the cervicalvertebra or other vertebrae.

It is to be understood that other mechanisms can be used to lock thelocking plate 1824 to the lateral mass plate 1820. For example, thelocking plate can include a probe with barbs that can be inserted into aport in the lateral mass plate. The barbs can become engaged in ribsthat define the side walls of the port in the lateral mass plate

In the preferred embodiment depicted in FIGS. 25A, 25B, the lateral massplate 1920 includes a recessed area 1922 for receiving the locking plate1924 so that the locking plate 1924 is flush with the upper surface 1925of the lateral mass plate 1920 when the probe 1926 is urged against thelateral mass screw 1940 and the keel 1928 is inserted into the lateralmass or the lamina of the vertebra. In the preferred embodiment depictedin FIGS. 25A, 25B, the shape and contours of the facet joint spacer orinter-facet joint spacer 1910 can facilitate insertion of the facetjoint spacer or inter-facet joint spacer 1910 into the cervical facetjoint. In this embodiment, the facet joint spacer or inter-facet jointspacer 1910 has a rounded distal end 1912. The distal end 1912 istapered in thickness to facilitate insertion. The tapered distal end1912 meets and is continuous with a proximal mid-section 1916 which, inthis preferred embodiment, has a uniform thickness, and is connectedflexibly, preferably with a hinge 1922, to the lateral mass plate 1920,as described above. The facet joint spacer (or insert) or inter-facetjoint spacer (or insert) 1910, with its proximal mid-section 1916 andtapered distal end 1912, is curved downward, causing a superior surface1913 of the facet joint spacer or inter-facet joint spacer 1910 to becurved. The curve can cause the superior surface 1913 to be convex, andthe convexity can vary among different implants 1900 to suit theanatomical structure of the cervical facet joint(s) of a patient. Aninferior surface 1915 accordingly can be preferably concave, flat, orconvex. The curved shape of the implant can fit the shape of a cervicalfacet joint, which is comprised of an inferior facet of an uppervertebra and a superior facet of a lower adjacent vertebra. The convexshape of the superior surface 1913 of the facet joint spacer orinter-facet joint spacer 1910 fits with a concave shape of the inferiorfacet of the upper cervical vertebrae. The concave shape of the inferiorsurface 1915 of the facet joint spacer or inter-facet joint spacer 1910fits with the convex shape of the superior facet of the cervicalvertebrae. The degree of convexity and concavity of the facet jointspacer or inter-facet joint inferior and superior surfaces can be variedto fit a patient's anatomy and the particular pairing of adjacentcervical vertebrae to be treated. For example, a less-curved facet jointspacer or inter-facet joint spacer 1910 can be used where the patient'scervical spinal anatomy is sized (as described below) and found to haveless convexity and concavity of the articular facets. Generally for thesame level the input for the right and left facet joint will besimilarly shaped. It is expected that the similarity of shape of thefacet joint spacer or inter-facet joint spacer and the smooth, flushsurfaces will allow distraction of the facet joint without loss ofmobility or damage to the bones of the cervical spine. Further, andpreferably, the width of the mid-section 1916 is from 1.5 mm to 2.5 mm.

Except as otherwise noted above, the embodiment shown in FIGS. 22A-24Bis similar to the embodiment shown in FIGS. 25A, 25B. Accordingly theremaining elements on the 1900 series of element numbers is preferablysubstantially similar to the described elements in the 1800 series ofelement numbers, as set forth above. Thus, by way of example, elements1923, 1928, 1929 and 1930 are similar, respective elements 1823, 1828,1829 and 1830.

FIG. 30 is a flow chart of the method of insertion of an implant of theinvention. The embodiment 1800 or 1900 of the present inventionpreferably is inserted in the following manner (only elements of theembodiment 1800 will be set forth herein, for purposes of the writtendescription of a method of the invention). First the facet joint isaccessed. A sizing tool 2200 (see FIGS. 29A-C) can be inserted to selectthe appropriate size of an implant of the invention for positioning inthe cervical facet joint. This step may be repeated as necessary with,if desired, different sizes of the tool 2200 until the appropriate sizeis determined. This sizing step also distracts the facet joint andsurrounding tissue in order to facilitate insertion of the implant.Then, the natural (made from animal bone) or artificial facet joint orinter-facet joint spacer 1810 is urged between the facets into the facetjoint. The facet itself is somewhat shaped like a ball and socket joint.Accordingly, in order to accommodate this shape, the natural orartificial facet joint spacer or inter-facet joint spacer 1810 can havea rounded leading edge shaped like a wedge or tissue expander to causedistraction of the facet joint as the natural or artificial facet jointspacer or inter-facet joint spacer is urged into the facet joint of thespine. The natural or artificial facet joint spacer or inter-facet jointspacer 1810 also includes the convex surface 1813 in order to more fullyaccommodate the shape of the facet joint of the spine. However, as setforth above and as depicted in FIG. 25B, it is possible in thealternative to have a curve-shaped natural or artificial facet jointspacer (or insert) or inter-facet joint spacer (or insert) 1910 with aconvex superior surface 1913 and a concave inferior surface 1915, thedistal end 1912 tapering to facilitate insertion, while the remainder ofthe natural or artificial facet joint spacer or inter-facet joint spacer1910, (i.e., the proximal section 1916) has a uniform thickness.

Once the natural or artificial facet joint spacer or inter-facet jointspacer 1810 is positioned, the lateral mass plate 1820 is pivoteddownward about the hinge 1822 adjacent to the vertebrae and preferablyto the lateral mass or to the lamina. Thus, the lateral mass plate 1820may be disposed at an angle relative to the natural or artificial facetjoint spacer or inter-facet joint spacer 1810 for a representative spineconfiguration. It is to be understood that as this embodiment is hingedthe final position of the lateral mass plate 1820 relative to thenatural or artificial facet joint spacer or inter-facet joint spacer1810 will depend on the actual spine configuration. It is to beunderstood that embodiments of the invention can be made without ahinge, as long as the connection between the natural or artificial facetjoint spacer or inter-facet joint spacer and the lateral mass plate isflexible enough to allow the lateral mass plate to be bent relative tothe natural or artificial facet joint spacer or inter-facet joint spacerin order to fit the anatomy of the patient. Once the lateral mass plate1820 is positioned, or prior to the positioning of the lateral massplate 1820, a bore can be drilled in the bone to accommodate the bonescrew 1824. Alternatively the screw 1824 can be self-tapping. The screwis then placed through the bore 1830 and secured to the bone, preferablythe lateral mass or the lamina, thereby holding the natural orartificial facet joint spacer or inter-facet joint spacer 1810 in place.In order to lock the bone screw 1824 in place and to lock the positionof the natural or artificial facet joint spacer or inter-facet jointspacer 1810 and the lateral mass plate 1820 in place, the locking plate1824 is positioned over the lateral mass plate 1820. So positioned, theprobe 1826 is positioned through the bore 1830 and against the head ofthe bone screw to keep the bone screw from moving. The keel 1828, havinga sharp chisel-shaped end, preferably can self-cut a groove in the boneso that the keel 1828 is locked into the bone as the keel 1828 isaligned by, and received in, a groove 1831 of the lateral mass plate1820. Alternatively, a groove can be pre-cut in the bone to receive thekeel 1828. As this occurs the bore 1829 of the locking plate 1824 alignswith the threaded bore 1831 of the lateral mass plate 1820 and a machinescrew can be inserted to lock the locking plate relative to the lateralmass plate. This locking prevents the lateral mass plate 1820 and thenatural or artificial facet joint spacer or inter-facet joint spacer1810 from rotating and, as previously indicated, prevents the bone screw1840 from backing out from the vertebra. Preferably the implant isbetween the C5 and C6 vertebrae level, or the C6 and C7 vertebrae level.It is noted that two implants preferably will be implanted at each levelbetween vertebrae. That is, an implant 1800 will be placed in a rightfacet joint and also in a left facet joint when viewed from a posteriorview point. This procedure can be used to increase or distract theforaminal area or dimension of the spine in an extension or in neutralposition (without having a deleterious effect on cervical lordosis) andreduce the pressure on the nerves and blood vessels. At the same timethis procedure preserves mobility of the facet joint.

FIGS. 26A-27B show a further embodiment of the implant of the invention,with the embodiment 2000 implanted in the cervical spine as depicted inFIGS. 27A and 27B. The implant 2000 comprises a first natural orartificial facet joint spacer (or insert) or inter-facet joint spacer(or insert) 2010 and a second natural or artificial facet joint spacer(or insert) or inter-facet joint spacer (or insert) 2010. Each naturalor artificial facet joint spacer or inter-facet joint spacer can have adistal end 2012 that is tapered or wedge-shaped in a way thatfacilitates insertion into the cervical facet joints on both sides oftwo adjacent cervical vertebrae at the same level. The naturalartificial facet joint spacers or inter-facet joint spacers further canbe dome-shaped, or convex on a superior surface 2013, to approximate theshape of the cervical facets of the cervical facet joints.

The first and second natural or artificial facet joint spacers orinter-facet joint spacers 2010 are bridged together by a collar 2015.The collar 2015 passes between the spinous processes of the adjacentcervical vertebrae. As can be seen in FIG. 26B, the implant canpreferably be “V” shaped or “boomerang” shaped. The entire implant 2000or the collar 2015 of the implant can be made of a flexible materialsuch as titanium, so that it is possible to bend the collar 2015 so thatit conforms preferably to the shape of the lateral mass or the lamina ofthe cervical vertebrae of the patient and thereby holds the implant inplace with the natural or artificial facet joint spacers or inter-facetjoint spacers 2010 inserted in the cervical facet joints. Bores 2029 arepreferably provided through implant 2000 adjacent to the natural orartificial facet joint spacer or inter-facet joint spacer 2010respectively. These bores 2029 can receive bone screws to position theimplant 2000 against the lateral mass or the lamina as shown in FIGS.27A, 27B. The description of the embodiment 2100, in FIGS. 28A, 28Bprovide further details concerning the method of affixing the implant2000 to the vertebrae. The implant 2100 also can be made of PEEK orother materials as described herein. Embodiment 2000 (the “boomerang”shape depicted in FIG. 27B) further can have a locking plate as, forexample, the locking plate 1824 in FIG. 22A. The locking plate forembodiment 2000 (not shown) can have the same features as locking plate1824, that is: (1) a probe 1826 that interacts with the bone screws toprevent the bone screws from backing out of the bone, the likelyconsequence of which would be displacement of the implant 2000; and (2)a keel 1828 with a chisel end to embed in the bone and thus to preventrotational displacement of the implant. However, given the collar 2015configuration of embodiment 2000, a chisel may not serve the samepurpose as with the embodiments set forth above, which lack a collarstabilized by two bone screws. Therefore, a locking plate on embodiment2000 can be provided without a keel.

FIGS. 28A and 28B depict a further embodiment of the implant of theinvention 2100. In this embodiment 2100, the collar 2115 can be made ofa flexible material such as titanium, of a substantially inflexiblematerial, or of other materials described herein. Substantialflexibility can also be derived from connecting a first natural orartificial facet joint spacer (or insert) or inter-facet joint spacer(or insert) 2110 with the collar 2115 using a first hinge 2117, andconnecting a second natural or artificial facet joint spacer orinter-facet joint spacer 2110 with the collar 2115 using a second hinge2117. Using the first hinge 2117 and the second hinge 2117, the collar2115 can be pivoted downward to conform to a particular patient'scervical spinal anatomy. In other words, the degree of pivoting willvary among different patients, and the first hinge 2117 and second hinge2117 allow the implant 2100 to accommodate the variance.

In the hinged embodiment 2100, and similar to the embodiment 2000, thecollar 2115 can have a first bore 2129 inferior to the first hinge 2117,and a second bore 2129 inferior to the second hinge 2117. A first bonescrew penetrates the first bore 2129 and into the lateral mass or thelamina, and the second bone screw penetrates the second bore 2129 andinto the lateral mass or the lamina, the first and second bone screwsserving to anchor the implant. A bore, preferably in the lateral mass,can be drilled for the first bone screw and for the second bone screw.Alternatively, the bone screws can be self-tapping. A first lockingplate similar to the plate 1924 (FIG. 25A) can be secured about the headof the first bone screw and a second locking plate can be secured aboutthe head of the second bone screw to prevent displacement of the firstand second bone screws 2140. The first locking plate can block the firstbone screw with a probe and the second locking plate can block to thesecond bone screw with a probe.

It should be noted that embodiments 2000 and 2100 also can be configuredfor accommodating treatment of cervical spinal stenosis and othercervical spine ailments where only a single cervical facet joint betweenadjacent vertebrae requires an implant, i.e., where treatment is limitedto one lateral facet joint. In that case, the collar 2015, 2115 extendsmedially without extending further to join a second natural orartificial facet joint spacer or inter-facet joint spacer 2010, 2110.For the hinged embodiment 2100, the implant comprises a single hinge2117, and the collar 2115 has only one bore 2129 to accept one bonescrew to secure the implant 2100.

FIGS. 29A-E, depict a sizing and distracting tool 2200 of the invention.Sizing tool 2200 has a handle 2203 and a distal head 2210 that is shapedas a natural or artificial facet joint spacer or inter-facet jointspacer (e.g., 1810) of an implant of the invention. That is, the head2210 preferably will have essentially the same features as the naturalor artificial facet joint spacer or inter-facet joint spacer 1810, butthe dimensions of the head 2210 will vary from one tool 2200 to thenext, in order to be able to use different versions of the sizing tool2200 to determine the dimensions of the cervical facet joint that is tobe treated and then to select an appropriately-sized implant. The head2210 preferably can be used to distract the facet joint prior to thestep of implanting the implant in the facet joint. In this regard, thehead 2210 is rounded at the most distal point 2212, and can be a taperedto facilitate insertion into a cervical facet joint. The head 2210 alsocan have a slightly convex superior surface 2213, the degree ofconvexity varying among different sizing tools 2200 in order todetermine the desired degree of convexity of an implant to be implantedin the cervical facet joint. The head 2210 may have a uniform thicknessalong a proximal mid-section 2216. Accordingly, the inferior surface2215 preferably can be concave. Alternatively, the proximal mid-section2212 may be convex on the superior surface 1813 without being uniform inthickness. Thus, the inferior surface 2215 can be flat or planar. Thehead also can be curved.

The head 2210 has a stop 2218 to prevent over-insertion of the head 2210of the sizing tool 2200 into the facet joint. The stop 2218 can be aridge that separates the head 2210 from the handle 2203. Alternatively,the stop 2218 can be any structure that prevents insertion beyond thestop 2218, including pegs, teeth, and the like.

Different sizing tools 2200 covering a range of dimensions of the head2210 can be inserted successively into a cervical facet joint to selectthe appropriate size of an implant to position in the cervical spine,with the appropriate convexity and concavity of natural or artificialfacet joint spacer or inter-facet joint spacer. Each preferably largerhead also can be used to distract the facet joint.

FIG. 31A depicts a posterior view of a further embodiment 2300 of theimplant of the invention. Embodiment 2300, as well as all of theembodiments herein, can benefit from some or all of the advantagesdescribed herein with regard to the other embodiments described herein.Further, in FIG. 31A, embodiment 2300 has a natural or artificial facetjoint spacer (or insert) or inter-facet joint spacer (or insert) 2310that can have a tapered or thinned distal end 2312 so that the distalend 2312 facilitates insertion of the natural or artificial facet jointspacer or inter-facet joint spacer 2310 into a cervical facet joint. Thedistal end 2312 can be rounded, as seen in the plan view of FIG. 31A, inorder to conform to the roundness of the facet joint. The natural orartificial facet joint spacer or inter-facet joint spacer 2310 furthercan be curved so that a superior surface 2313 of the natural orartificial facet joint spacer or inter-facet joint spacer 2310 isconvex, and an inferior surface 2315 is concave, to approximate thenatural shape of the cervical facet joint that is to receive the implant2300. The curve can have a uniform thickness, or it can have a variedthickness. Further, the lateral edges of the natural or artificial facetjoint spacer or inter-facet joint spacer 2310 are curved or rounded, fordistribution of load-bearing stress. As with other embodiments describedherein, the natural or artificial facet joint spacer or inter-facetjoint spacer 2310 also can be made of a flexible, biocompatiblematerial, such as PEEK, to maintain joint mobility and flexibility.

The natural or artificial facet joint spacer or inter-facet joint spacer2310 is connected flexibly with a lateral mass plate 2320, the flexibleconnection preferably being a hinge 2322. As seen in the plan view ofFIG. 31A, the implant 2300 is substantially hour-glass shaped. Thisshape, as well as the shape of FIG. 32, will be discussed further below.The hinge 2322 is narrower than the natural or artificial facet jointspacer or inter-facet joint spacer 2310, with the hinge 2322 sitting atsubstantially the isthmus 2317 between the natural or artificial facetjoint spacer or inter-facet joint spacer 2310 and the lateral mass plate2320. The curved edges, or fillets, about the hinge 2322 serve todistribute more evenly the load-bearing stress on the implant 2300, andthus prevent concentrating the stress about the edges.

The hinge 2322 allows the implant 2300 to bend at the hinge 2322,bringing a lateral mass plate 2320 adjacent to the lateral mass and/orlamina of the patient's spine, and to conform to a particular patient'sanatomy. The lateral mass plate 2320 is made of a biocompatible flexiblematerial, preferably titanium or any other biocompatible flexiblematerial as described herein, for example PEEK, that will support theuse of bone screws and other hardware, as described below. The lateralmass plate 2320 bends downward at the hinge 2322 over a wide range ofangles relative to the natural or artificial facet joint spacer orinter-facet joint spacer 2310, and preferably at an angle of more than90 degrees, and this flexibility facilitates positioning and insertionof the natural or artificial facet joint spacer or inter-facet jointspacer. This flexibility of the lateral mass plate 2320 relative to thenatural or artificial facet joint spacer or inter-facet joint spacer2310 further facilitates positioning of the lateral mass plate relativeto the lateral mass and/or the lamina of the patient's spine. Once thelateral mass plate 2320 is positioned adjacent to the bone, preferablythe lateral mass of a cervical vertebra, a first bone screw, such asbone screw 1840, can be inserted through a first bore 2330 through thelateral mass plate 2320 and embedded into the bone of the lateral massof the cervical vertebra.

The lateral mass plate 2320 further comprises a second bore 2329 whichis preferably positioned medially, relative to the first bore 2330.Thus, viewing the implant from a posterior perspective as in FIG. 31A,the second bore 2329 in the lateral mass plate 2320 can be positionedeither to the left or to the right of the first bore 2330. The positionof the second bore 2329 will depend upon whether the implant 2300 isintended to be inserted into a cervical facet joint on the left or rightside of a patient. Specifically, an implant 2300 to be inserted into aright-side cervical facet joint (i.e., the patient's rights side) willhave a second bore 2329 positioned to the left of the first bore 2330 asin FIG. 31A, when implant 2300 is viewed from a posterior perspective,while an implant 2300 to be inserted into a left-side cervical facetjoint will have a second bore 2329 positioned to the right of the firstbore 2330, when implant 2300 is viewed from a posterior perspective.

The second bore 2329 through the lateral mass plate 2320 is adapted toaccept a second screw 2390 (FIG. 31B), which preferably is a lockingscrew with a chisel point 2391. The locking screw 2390 is received bythe second bore 2329 and the chisel point 2391 self-cuts a bore into thebone. The locking screw 2390 preferably is inserted through the secondbore 2329 and embedded in the bone, after the bone screw is embedded inthe bone through the first bore 2330. The position of the second bore2329, i.e., medial to the first bore 2330, positions the locking screw2390 so that it embeds in stronger bone tissue than if the second bore2329 were located more laterally. The locking screw, in combination withthe bone screw, prevents rotational and/or backward displacement of theimplant 2300. As the locking screw 2390 is received by the second bore2329, the head 2392 of the locking screw 2390 aligns with the head ofthe first bone screw in the first bore 2330, blocking the head of thefirst bone screw to prevent the first bone screw from backing out of thebone of the vertebra and the first bore 2330.

FIG. 32 depicts a further embodiment 2400 of the implant of theinvention, from a posterior view. Embodiment 2400 is adapted to beimplanted in a manner that preserves the anatomy of the cervical facetjoint, in particular, the soft tissues around the cervical facet joint,including the joint capsule.

Implant 2400, like implant 2300 and other implants disclosed above, hasa natural or artificial facet joint spacer or inter-facet joint spacer2410, flexibly connected, preferably by a hinge 2422, to a lateral massplate 2420. As can be seen in FIG. 32, the implant 2400 including thenatural or artificial facet joint spacer or inter-facet joint spacer2410 and the hinge 2422 is substantially “P” shaped. As explained below,its “P” shape assists in the insertion of the implant 2400 into thefacet joint with most of the facet capsule and facet capsule ligamentand other soft tissue associated with the facet joint still left intact.The natural or artificial facet joint spacer or inter-facet jointspacer, as above for implant 2300 and the other implants disclosedabove, can have a superior surface 2413 of the natural or artificialfacet joint spacer or inter-facet joint spacer 2410 that is convex, andan inferior surface 2415 that is concave, or any appropriate shaping toapproximate the natural shape of the cervical facet joint that is toreceive the implant 2400. The thickness of the natural or artificialfacet joint spacer or inter-facet joint spacer 2410 can be uniform, orvaried. The natural or artificial facet joint spacer or inter-facetjoint spacer 2410 also can be made of a flexible, biocompatiblematerial, such as PEEK, to maintain joint mobility and flexibility. Thehinge 2422 can have smooth, rounded edges, for distribution of loadstress, as disclosed above. Other features and advantages of the otherembodiments can be, if desired, incorporated into the design of theembodiment of FIG. 32. For example, the natural or artificial facetjoint spacer or inter-facet joint spacer 2410 further can have a taperedor thinned edge 2412 so that the edge 2412 facilitates insertion of thenatural or artificial facet joint spacer or inter-facet joint spacer2410 into a cervical facet joint. The edge 2412 can be curved. In thisembodiment 2400, however, the thinned edge 2412 of the natural orartificial facet joint spacer or inter-facet joint spacer 2410preferably is not at the distal end of the natural or artificial facetjoint spacer or inter-facet joint spacer 2410 as is the thinned edge2312 of the natural or artificial facet joint spacer or inter-facetjoint spacer 2310; rather, the thinned edge 2412 preferably ispositioned laterally, toward the hinge 2422 of the implant 2400. Thethinned edge 2412 coincides substantially with a lateral curvature 2440of the natural or artificial facet joint spacer or inter-facet jointspacer 2410, which is pronounced relative to the curvature on the medialside of the implant 2400, i.e., a “P” shape. In other words, the curvedpart of the head of the “P” 2440 corresponds to the thinned edge 2412,and serves as the leading edge of the implant 2400 to begin insertion ofthe natural or artificial facet joint spacer or inter-facet joint spacer2410 into a cervical facet joint, preferably through an incision in thesoft tissue of the facet joint. The “P” shape narrows at isthmus 2417where the natural or artificial facet joint spacer or inter-facet jointspacer 2410 that is joined by the hinge 2422 with the lateral mass plate2420. The smooth or rounded edges or fillets serve to distributestresses on the implant 2400. The above described “P” shape of implant2400 allows the implant 2400 to be pivoted into place into a facet jointas described below. The thinned edge 2412 and leading lateral curvature2440 of the natural or artificial facet joint spacer or inter-facetjoint spacer 2410 are adapted to facilitate urging implant 2400 into thecervical facet joint, through the incision in the joint capsule. Theimplant 2400 then is pivoted into position so that the lateral massplate 2420 can be bent downward, relative to the natural or artificialfacet joint spacer or inter-facet joint spacer 2410, to align with andlie adjacent to the lateral mass and/or the lamina. The lateral massplate 2420 is then fastened to the bone. The lateral mass plate 2420 ofimplant 2400, like the lateral mass plate for implant 2300, is flexiblyconnected, preferably by the smooth-edged hinge 2422, to the natural orartificial facet joint spacer or inter-facet joint spacer 2410 at thenarrow lower part of the artificial facet joint. The lateral mass plate2420 is made of a biocompatible flexible material, preferably titaniumor any other biocompatible flexible material such as PEEK that willsupport the use of bone screws and other hardware, as described below.As with the facet joint spacer, the lateral mass plate of any of theseembodiments can be made of a natural animal bone.

The lateral mass plate 2420 bends downward at a wide range of anglesrelative to the natural or artificial facet joint spacer or inter-facetjoint spacer 2410, and preferably at an angle of more than 90 degrees.The flexibility of the lateral mass plate 2420 relative to the naturalor artificial facet joint spacer or inter-facet joint spacer 2410further facilitates positioning of the lateral mass plate 2420 relativeto the lateral mass and/or the lamina of the patient's spine.

Like embodiment 2300, described above, the lateral mass plate 2420 hasfirst bore 2430, which is adapted to receive a bone screw 2440, to helpanchor implant 2400 in position. The lateral mass plate 2420 furtherincludes a second bore 2429 adapted to be positioned medially, relativeto the first bore 2430, as disclosed above for implant 2300. Theposition of the second bore 2429, when viewing implant 2400 from aposterior perspective (FIG. 32), will depend upon whether implant 2400is intended to be implanted into a left-side or right-side cervicalfacet joint of a patient. Thus, implant 2400 with the second bore 2429positioned to the left of the first bore 2430 is intended to beimplanted in a right-side cervical facet joint of a patient, as depictedin FIG. 32, while an implant 2400 with a second bore 2429 positioned tothe right of the first bore 2430 is intended to be implanted in aleft-side cervical facet joint of a patient.

The second bore 2429 through the lateral mass plate 2420 is adapted toreceive a second screw 2490 with head 2492, which preferably is alocking screw with a chisel point, such as screw 2390. The function andpurpose of the bone screw disposed through bore 2430 and the lockingscrew disposed through bore 2429 are as described above with respect tothe implant 2300.

The present invention further includes a method of implanting theimplant 2400 (FIGS. 33A, 33B). To insert the natural or artificial facetjoint spacer or inter-facet joint spacer 2410, a facet joint is accessedand an incision or a pair of incisions is made in the capsular ligament,the joint capsule, and the synovial membrane so that the thinned edge2412 of the implant 2400 can be urged into the cervical facet jointthrough these tissues. The capsular ligament and the joint capsule andother soft tissues around the cervical facet joint are allowed to remainsubstantially intact, except for the small incision, and will be suturedand allowed to heal around the implant 2400. If desired, the cervicalfacet joint can be distracted prior to urging the curved section 2440with the thinned edge 2412 of the natural or artificial facet jointspacer or inter-facet joint spacer 2410 into the cervical facet joint.Once the curved section 2440 of the natural or artificial facet jointspacer or inter-facet joint spacer 2410 with the thinned edge 2412 isurged into the cervical facet joint, implant 2400 is pivoted, preferablyabout 90 degrees, so that the second bore 2429 is placed mediallyrelative to the first bore 2430. This allows the natural or artificialfacet joint spacer or inter-facet joint spacer 2410 to be positioned inthe facet joint. It is noted that the overall size, including theisthmus 2417, of the natural or artificial fact joint spacer orinter-facet joint spacer 2410, as that of 2310, can be somewhat smallerthan in prior embodiments to allow the natural or artificial facet jointspacer or inter-facet joint spacer to be positioned within the edges ofthe facet joint with the joint capsule substantially intact. The lateralmass plate 2420 then can be bent downward about the hinge 2422 intoposition adjacent the lateral mass or lamina of the spine of thepatient, which position will depend upon the anatomy of an individualpatient's cervical spine.

Once the lateral mass plate 2420 is positioned adjacent to the bone,preferably the lateral mass of a cervical vertebra, a first bone screwcan be inserted through the first bore 2430 through the lateral massplate 2420 and become embedded into the bone of the lateral mass of thecervical vertebra to anchor the implant 2400. After the bone screw isembedded, a locking screw is inserted through the second bore 2429 ofthe lateral mass plate 2420, the second bore 2429 medial to the firstbore 2430. The locking screw has a chisel end that allows the lockingscrew to dig into the bone without use of a tool to pre-cut a bore.Alternatively, a bore can be pre-cut and a locking screw without achisel end can be used. As the locking screw is embedded in the bone,the locking head of the locking screw is brought into proximity with thehead of the bone screw to block its backward movement so that theimplant 2400 remains anchored with the bone screw, i.e., so that thebone screw cannot back out of the bone. The embedded locking screw alsoserves to prevent rotational displacement of implant 2400, whileblocking backward displacement of the first bone screw.

Referring to FIGS. 34A through 36B, a still further embodiment of animplant 2500 in accordance with the present invention can include anatural or artificial facet joint spacer (or insert) or inter-facetjoint spacer (or insert) 2510 connected with a lateral mass plate (alsoreferred to herein as an anchoring plate) 2520 by a spheroidal jointarrangement 2538 or otherwise shaped multiple direction articulationjoint arrangement. The natural or artificial facet joint spacer orinter-facet joint spacer 2510 has a load bearing structure sized andshaped to distribute, as desired, a load applied by opposing surfaces ofsuperior and inferior facets to one another. As shown, the load bearingstructure has a saucer shape, but as described in further detail below(and as described in previous embodiments above), in other embodimentsthe load bearing structure can have some other shape so long as adesired load distribution and separation between superior and inferiorfacets is achieved. The natural or artificial facet joint spacer orinter-facet joint spacer 2510 includes a handle-like structure connectedwith the load bearing surface, the handle-like structure necking at anisthmus 2517 and terminating at a pivot end 2526. In an embodiment, thepivot end 2526 is substantially spherical, ovoidal, or similarly roundedin shape. As further described below, the natural or artificial facetjoint spacer or inter-facet joint spacer 2510 can comprise a flexiblematerial, for example a biocompatible polymer such as PEEK, or a morerigid material, for example a biocompatible metal such as titanium. Asshown, the lateral mass plate 2520 has a generally square shape withrounded corners; however, in other embodiments the lateral mass plate2520 can have any number of shapes so long as the lateral mass plate2520 provides sufficient support for anchoring the implant 2500 inposition and so long as the lateral mass plate 2520 allows a desiredrange of motion for the natural or artificial facet joint spacer orinter-facet joint spacer 2510. The lateral mass plate 2520 includes acavity 2527 within which the pivot end 2526 is held. The spheroidaljoint arrangement 2538 comprises the pivot end 2526 and the cavity 2527and as described below allows the natural or artificial facet jointspacer or inter-facet joint spacer 2510 to tilt and swivel relative tothe lateral mass plate 2520.

FIG. 34A is a posterior view showing a posterior face 2532 of thelateral mass plate 2520, while FIG. 34B is an anterior view showing ananterior face 2534 of the lateral mass plate 2520. The lateral massplate 2520 includes an anterior notch 2524 (see FIG. 35) or otherindentation formed along the edge of the anterior face 2534 and aposterior notch 2522 or other indentation formed along the posteriorface 2532. The posterior and anterior notches 2522, 2524 are generallyaligned with one another along the edge of the lateral mass plate 2520and are connected with the cavity 2527. The notches 2522, 2524 confinemovement of the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 in the anterior and posterior directions relative tothe lateral mass plate 2520, allowing the natural or artificial facetjoint spacer or inter-facet joint spacer 2510 to tilt at varying degreesof angle in an anterior and posterior direction. Referring to FIG. 35,the anterior notch 2524 can have a narrower width than the posteriornotch 2522 which is sized to provide the pivot end 2526 of the naturalor artificial facet joint spacer or inter-facet joint spacer 2510 withaccess to the cavity 2527 so that the pivot end 2526 can be insertedinto the cavity 2527. Once the pivot end 2526 is positioned within thecavity 2527 a plug 2528 can be mated with the lateral mass plate 2520 tolock the pivot end 2526 in place within the cavity 2527 and to furtherlimit freedom of movement of the natural or artificial facet jointspacer or inter-facet joint spacer 2510, particularly limiting tiltingof the natural or artificial facet joint spacer or inter-facet jointspacer 2510 in a posterior direction. The plug 2528 can be press fit tothe posterior notch 2522 and further welded or otherwise fixedlyfastened with the lateral mass plate 2520. A physician can select anappropriate and/or desired natural or artificial facet joint spacer orinter-facet joint spacer 2510, lateral mass plate 2520, and plug 2528according to the motion segment targeted for implantation and/or theparticular anatomy of the patient. Once an appropriate combination ofcomponents is identified, the natural or artificial facet joint spaceror inter-facet joint spacer 2510 and the lateral mass plate 2520 can bemated, and the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 can be locked in place by the plug 2528.

As can further be seen in FIGS. 34A through 35 the lateral mass plate2520 has a first bore 2530 therethrough. The first bore 2530 can accepta bone screw 2540 (also referred to herein as a lateral mass screw) tosecure the lateral mass plate 2520 preferably to the lateral mass,lamina, or alternatively to another part of the spine, and thus toanchor the implant 2500. The lateral mass screw 2540 preferably has ahead 2542 that can accept a tool chosen for the surgical procedurewhether a wrench, screwdriver, or other tool. The lateral mass plate2520 further has a second bore 2529 which is preferably positionedmedially, relative to the first bore 2530. Referring to FIG. 34A, thesecond bore 2529 in the lateral mass plate 2520 can be positioned eitherto the left or to the right of the first bore 2530. The position of thesecond bore 2529 will depend upon whether the implant 2500 is intendedto be inserted into a cervical facet joint on the left or right side ofa patient. Specifically, an implant 2500 to be inserted into aright-side cervical facet joint (i.e., the patient's rights side) willhave a second bore 2529 positioned to the left of the first bore 2530 asin FIG. 34A, when implant 2500 is viewed from a posterior perspective,while an implant 2500 to be inserted into a left-side cervical facetjoint will have a second bore 2529 positioned to the right of the firstbore 2530, when implant 2500 is viewed from a posterior perspective.

The second bore 2529 through the lateral mass plate 2520 is adapted toaccept a second screw 2590 which preferably is a locking screw having achisel point 2591. The locking screw 2590 is received by the second bore2529 and the chisel point 2591 self-cuts a bore into the bone. Thelocking screw 2590 is preferably inserted through the second bore 2529and embedded in the bone after the bone screw 2540 is embedded in thebone through the first bore 2530. The medial position of the second bore2529 relative to the first bore 2530 positions the locking screw 2590 sothat it embeds in stronger bone tissue than if the second bore 2529 werelocated more laterally. The locking screw 2590, in combination with thebone screw 2540, prevents rotational and/or backward displacement of thelateral mass plate 2520. As the locking screw 2590 is received by thesecond bore 2529, the head 2592 of the locking screw 2590 aligns withthe head 2542 of the first bone screw 2540 in the first bore 2530,blocking the head 2542 of the first bone screw 2540 to prevent the firstbone screw 2540 from backing out of the bone of the vertebra and thefirst bore 2530. The posterior face 2532 can include a recessed portion2539, and/or the second bore 2529 can be countersunk, so that thelocking screw 2590 does not protrude farther from the posterior face2532 than desired.

In a preferred embodiment (as shown in FIGS. 34A-37), the spheroidaljoint arrangement 2538 includes a spherical pivot end 2526 and a cavity2527 having a shape approximately conforming to the spherical pivot end2526 so that the spheroidal joint arrangement 2538 is a ball-in-socketarrangement. The ball-in-socket arrangement 2538 allows the natural orartificial facet joint spacer or inter-facet joint spacer 2510 to movefreely relative to the lateral mass plate 2520 where the natural orartificial facet joint spacer or inter-facet joint spacer 2510 isunobstructed by the lateral mass plate 2520. For example, as shown inFIG. 36A the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 can tilt in an anterior direction (to position 1, forexample) and can tilt in a posterior direction (to position 2, forexample). As the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 tilts in an anterior direction, the isthmus 2517 moveswithin the anterior notch 2524 so that the natural or artificial facetjoint spacer or inter-facet joint spacer 2510 can continue tiltingwithout obstruction. Conversely, as the natural or artificial facetjoint spacer or inter-facet joint spacer 2510 tilts in a posteriordirection (to position 2, for example), the isthmus 2517 contacts theplug 2528, limiting the amount of tilt of the natural or artificialfacet joint spacer or inter-facet joint spacer 2510 in a posteriordirection.

Referring to FIG. 36B, the ball-and-socket arrangement allows thenatural or artificial facet joint spacer or inter-facet joint spacer2510 to swivel (to position 3, for example) relative to the lateral massplate 2520, potentially providing a more conformal arrangement of thenatural or artificial facet joint spacer or inter-facet joint spacer2510 with the surfaces of the superior and inferior facets. Further, theability of the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 to swivel can increase options for lateral mass plate2520 anchor positions. A physician can anchor the lateral mass plate2520 in a more conformal or advantageous orientation and/or positionalong the lateral mass, for example, by altering the arrangement of thelateral mass plate 2520 relative to the natural or artificial facetjoint spacer or inter-facet joint spacer 2510. The amount of swivelingaccommodated (and the degree of freedom of movement accommodated ingeneral) depends on the geometries of the components. For example, wherethe isthmus 2517 is sufficiently narrow and long in length, a greaterdegree of swiveling in combination with tilt can be achieved, or, forexample, where the plug 2528 extends over a portion of the natural orartificial facet joint spacer or inter-facet joint spacer 2510, as shownin FIGS. 36A and 36B, the amount of tilt possible in the posteriordirection can be limited. One of ordinary skill in the art willappreciate that the freedom of movement of the natural or artificialfacet joint spacer or inter-facet joint spacer 2510 relative to thelateral mass plate 2520 is limited substantially or wholly by thegeometries of the components, and therefore can be substantially alteredto achieve a desired range of movement. The ball-and-socket arrangementneed not include a ball that extends from the natural or artificialfacet joint spacer or inter-facet joint spacer and a socket that isformed in the lateral mass plate. For example, the ball of such a jointcan extend from a locking or anchoring plate and the socket can beincluded in the natural or artificial facet joint spacer or inter-facetjoint spacer. Further, while the preferred embodiment has been describedas a ball-and-socket arrangement, other arrangements can be employedwith varied results. It should not be inferred that embodiments inaccordance with the present invention need include a spheroidal shapedend mated with a rounded cavity. The scope of the present invention isnot intended to be limited to ball-and-socket arrangements, but ratheris intended to encompass all such arrangements that provide a pluralityof degrees of freedom of movement and substitutability of components.

Referring again to FIGS. 36A and 36B, the load bearing structure of thenatural or artificial facet joint spacer or inter-facet joint spacer2510 includes a superior surface 2513 having a generally convex shapeand an inferior surface 2514 having a slightly concave shape. The shapeof the load bearing structure is intended to approximate a shape ofopposing surfaces of the superior and inferior facets. The shape of thesuperior and inferior surfaces 2513, 2514 can vary between motionsegments and between patients. For example, as shown in FIG. 37, wherethe cervical vertebra includes an inferior facet having a substantiallyconvex natural surface, a physician may select a natural or artificialfacet joint spacer or inter-facet joint spacer 2610 including a loadbearing structure with an inferior surface 2614 having a more concaveshape combined with a lateral mass plate 2620 having a bone screw 2640more appropriately sized for the particular lateral mass to which itwill be fixed. (As shown the bone screw 2640 has a shorter length andwider diameter.) A physician can be provided with natural or artificialfacet joint spacers or inter-facet joint spacers having a multiplicityof load bearing structure shapes. As mentioned above, the ability tomatch different natural or artificial facet joint spacers or inter-facetjoint spacers with different lateral mass plates can improve aphysician's ability to provide appropriate treatment for a patient, andcan further provide the physician flexibility to reconfigure an implantonce a surgical site has been exposed and the physician makes adetermination that a different combination of components is appropriate.

In yet another embodiment, the spheroidal joint arrangement 2538 ofFIGS. 34A-37 can be applied to collar structures, for example as shownin FIGS. 26A-27B so that the natural or artificial facet joint spacersor inter-facet joint spacers at each end of the collar structure includean increased range of motion to improve surface matching between thenatural or artificial facet joint spacers or inter-facet joint spacersand the surfaces of the superior and inferior facets (i.e., increasingthe amount of facet surface area contacting the natural or artificialfacet joint spacers or inter-facet joint spacers).

FIG. 38 is a flow chart of an embodiment of a method in accordance withthe present invention for implanting an implant as described in FIGS.34A through 37. An incision must first be made to expose the surgicalsite and access the targeted facet joint (Step 2500). Once the facetjoint is made accessible, the facet joint can be sized and distracted(Step 2502). A sizing tool 2200 (for example, see FIGS. 29A-C) can beinserted to select the appropriate size of an implant 2500 of theinvention for positioning in the cervical facet joint. This step may berepeated as necessary with, if desired, different sizes of the tool 2200until the appropriate size is determined. This sizing step alsodistracts the facet joint and surrounding tissue in order to facilitateinsertion of the implant 2500. Once the appropriate size is determine,the physician can select an appropriate natural or artificial facetjoint spacer or inter-facet joint spacer 2510 with the lateral massplate 2520 (Step 2504). The natural or artificial facet joint spacer orinter-facet joint spacer 2510 can then be urged between the facets intothe facet joint (Step 2510). The facet itself is somewhat shaped like aball and socket joint. Accordingly, in order to accommodate this shape,the natural or artificial joint spacer or inter-facet joint spacer 2510can have a rounded leading edge shaped like a wedge or tissue expanderto cause distraction of the facet joint as the natural or artificialfacet joint spacer or inter-facet joint spacer is urged into the facetjoint of the spine. The natural or artificial facet joint spacer orinter-facet joint spacer 2510 also includes the convex superior surface2513 in order to more fully accommodate the shape of the facet joint ofthe spine. However, as set forth above and as depicted in FIG. 37, it ispossible in the alternative to have a curve-shaped natural or artificialfacet joint spacer or inter-facet joint spacer 2610 with a convexsuperior surface 2613 and a concave inferior surface 2614, the distalend of the natural or artificial facet joint spacer or inter-facet jointspacer 2610 tapering to facilitate insertion, while the remainder of thenatural or artificial facet joint spacer or inter-facet joint spacer2610 has a uniform thickness.

Once the natural or artificial joint spacer or inter-facet joint spacer2510 is positioned, the lateral mass plate 2520 is tilted and/orswiveled so that the lateral mass plate 2520 is adjacent to thevertebrae and preferably to the lateral mass or to the lamina (Step2512). Thus the lateral mass plate 2520 may be disposed at an anglerelative to the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 for a representative spine configuration. It is to beunderstood that the final position of the lateral mass plate 2520relative to the natural or artificial facet joint spacer or inter-facetjoint spacer 2510 will depend on the actual spine configuration. Oncethe lateral mass plate 2520 is positioned, or prior to the positioningof the lateral mass plate 2520, a bore can be drilled in the bone toaccommodate the bone screw 2540. Alternatively the screw 2540 can beself-tapping. The screw 2540 is then placed through the first bore 2530and secured to the bone, preferably the lateral mass or the lamina,thereby holding the natural or artificial facet joint spacer orinter-facet joint spacer 2510 in place (Step 2514). In order to lock thebone screw 2540 in place and to lock the position of the natural orartificial facet joint spacer or inter-facet joint spacer 2510 and thelateral mass plate 2520 in place, a self-tapping locking screw 2590 ispositioned within a second bore 2529 of the lateral mass plate 2520 andsecured to the bone, thereby resisting undesirable movement of thelateral mass plate 2520 (Step 2516). A head 2592 of the locking screw2590 can further block movement of the bone screw 2540 by trapping thebone screw head 2542 between the locking screw head 2592 and the firstbore 2530. The locking screw 2590 therefore prevents the lateral massplate 2520 and the natural or artificial facet joint spacer orinter-facet joint spacer 2510 from rotating and, as previouslyindicated, prevents the bone screw 2540 from backing out from thevertebra. Preferably the implant is between the C5 and C6 vertebraelevel, or the C6 and C7 vertebrae level. It is noted that two implantspreferably will be implanted at each level between vertebrae. That is,an implant will be placed in a right facet joint and also in a leftfacet joint when viewed from a posterior view point. This procedure canbe used to increase or distract the foraminal area or dimension of thespine in an extension or in neutral position (without having adeleterious effect on cervical lordosis) and reduce the pressure on thenerves and blood vessels. At the same time this procedure preservesmobility of the facet joint.

Materials for Use in Implants of the Present Invention

As alluded to above, and as described in further detail as follows, insome embodiments, the implant, and components of the implant (i.e., alateral mass plate, a bone screw, a locking screw, etc.) can befabricated from medical grade metals such as titanium, stainless steel,cobalt chrome, and alloys thereof, or other suitable implant materialhaving similar high strength and biocompatible properties. Additionally,the implant can be at least partially fabricated from a shape memorymetal, for example Nitinol, which is a combination of titanium andnickel. Such materials are typically radiopaque, and appear during x-rayimaging, and other types of imaging. Implants in accordance with thepresent invention, and/or portions thereof (in particular an artificialfacet joint) can also be fabricated from somewhat flexible and/ordeflectable material. In these embodiments, the implant and/or portionsthereof can be fabricated in whole or in part from medical gradebiocompatible polymers, copolymers, blends, and composites of polymers.A copolymer is a polymer derived from more than one species of monomer.A polymer composite is a heterogeneous combination of two or morematerials, wherein the constituents are not miscible, and thereforeexhibit an interface between one another. A polymer blend is amacroscopically homogeneous mixture of two or more different species ofpolymer. Many polymers, copolymers, blends, and composites of polymersare radiolucent and do not appear during x-ray or other types ofimaging. Implants comprising such materials can provide a physician witha less obstructed view of the spine under imaging, than with an implantcomprising radiopaque materials entirely. However, the implant need notcomprise any radiolucent materials.

One group of biocompatible polymers is the polyaryletherketone groupwhich has several members including polyetheretherketone (PEEK), andpolyetherketoneketone (PEKK). PEEK is proven as a durable material forimplants, and meets the criterion of biocompatibility. Medical gradePEEK is available from Victrex Corporation of Lancashire, Great Britainunder the product name PEEK-OPTIMA. Medical grade PEKK is available fromOxford Performance Materials under the name OXPEKK, and also fromCoorsTek under the name BioPEKK. These medical grade materials are alsoavailable as reinforced polymer resins, such reinforced resinsdisplaying even greater material strength. In an embodiment, the implantcan be fabricated from PEEK 450G, which is an unfilled PEEK approved formedical implantation available from Victrex. Other sources of thismaterial include Gharda located in Panoli, India. PEEK 450G has thefollowing approximate properties:

Property Value Density 1.3 g/cc Rockwell M 99 Rockwell R 126 TensileStrength 97 MPa Modulus of Elasticity 3.5 GPa Flexural Modulus 4.1 GPaPEEK 450G has appropriate physical and mechanical properties and issuitable for carrying and spreading a physical load between the adjacentspinous processes. The implant and/or portions thereof can be formed byextrusion, injection, compression molding and/or machining techniques.

It should be noted that the material selected can also be filled.Fillers can be added to a polymer, copolymer, polymer blend, or polymercomposite to reinforce a polymeric material. Fillers are added to modifyproperties such as mechanical, optical, and thermal properties. Forexample, carbon fibers can be added to reinforce polymers mechanicallyto enhance strength for certain uses, such as for load bearing devices.In some embodiments, other grades of PEEK are available and contemplatedfor use in implants in accordance with the present invention, such as30% glass-filled or 30% carbon-filled grades, provided such materialsare cleared for use in implantable devices by the FDA, or otherregulatory body. Glass-filled PEEK reduces the expansion rate andincreases the flexural modulus of PEEK relative to unfilled PEEK. Theresulting product is known to be ideal for improved strength, stiffness,or stability. Carbon-filled PEEK is known to have enhanced compressivestrength and stiffness, and a lower expansion rate relative to unfilledPEEK. Carbon-filled PEEK also offers wear resistance and load carryingcapability.

As will be appreciated, other suitable similarly biocompatiblethermoplastic or thermoplastic polycondensate materials that resistfatigue, have good memory, are flexible, and/or deflectable, have verylow moisture absorption, and good wear and/or abrasion resistance, canbe used without departing from the scope of the invention. As mentioned,the implant can be comprised of polyetherketoneketone (PEKK). Othermaterial that can be used include polyetherketone (PEK),polyetherketoneetherketoneketone (PEKEKK), polyetheretherketoneketone(PEEKK), and generally a polyaryletheretherketone. Further, otherpolyketones can be used as well as other thermoplastics. Reference toappropriate polymers that can be used in the implant can be made to thefollowing documents, all of which are incorporated herein by reference.These documents include: PCT Publication WO 02/02158 A1, dated Jan. 10,2002, entitled “Bio-Compatible Polymeric Materials;” PCT Publication WO02/00275 A1, dated Jan. 3, 2002, entitled “Bio-Compatible PolymericMaterials;” and, PCT Publication WO 02/00270 A1, dated Jan. 3, 2002,entitled “Bio-Compatible Polymeric Materials.” Other materials such asBionate®, polycarbonate urethane, available from the Polymer TechnologyGroup, Berkeley, Calif., may also be appropriate because of the goodoxidative stability, biocompatibility, mechanical strength and abrasionresistance. Other thermoplastic materials and other high molecularweight polymers can be used. Further, the embodiments hereof can be madeat least in part from a natural animal bone material.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many modifications and variations will be apparent to practitionersskilled in this art. The embodiments were chosen and described in orderto explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the following claims and theirequivalents.

What is claimed:
 1. A facet joint implant that addresses spinal stenosisand other ailments of a spine while maintaining mobility of a facetjoint, the implant comprising: an anchoring plate configured to anchorto a vertebra; a facet joint spacer sized and shaped to fit between asuperior facet and an inferior facet forming the facet joint; and amultiple direction articulation joint connecting the anchoring plate tothe facet joint spacer and located so that when the facet joint spaceris positioned between the superior facet and the inferior facet aportion of the multiple direction articulation joint is outside of thefacet joint, wherein the multiple direction articulation joint includesa cavity and a notch associated with one of the anchoring plate and thefacet joint spacer and a ball-shaped end associated with the other ofthe anchoring plate and the facet joint spacer, wherein the ball-shapedend is positionable within the cavity via the notch formed in the one ofthe anchoring plate and the facet joint spacer having the cavity.
 2. Theimplant of claim 1, wherein the multiple direction articulation joint isa ball-and-socket joint.
 3. The implant of claim 2, wherein the multipledirection articulation joint includes: the cavity with the facet jointspacer; and the ball-shaped end extending from the anchoring plate andpositioned in the cavity of the facet joint spacer.
 4. The implant ofclaim 1, wherein the multiple direction articulation joint includes: thecavity with the anchoring plate; and the ball-shaped end extending fromthe facet joint spacer and positioned in the cavity of the anchoringplate.
 5. The implant of claim 1, further comprising: a locking screw; abone screw; wherein: the anchoring plate further includes a first boreand a second bore; the bone screw is receivable within the first bore;and the locking screw is receivable within the second bore.
 6. Theimplant of claim 5, wherein the locking screw has a head that blocks thebone screw from at least one of a backward displacement and a rotationaldisplacement.
 7. The implant of claim 5, wherein the locking screwfurther comprises a chisel-point end, wherein the chisel point endself-cuts the locking screw into the vertebra.
 8. The implant of claim5, wherein the locking screw is positioned medially, relative to thebone screw in a patient.
 9. The implant of claim 1, further comprising alocking member adapted to engage the notch to lock the ball-shaped endwithin the cavity.
 10. A facet joint implant that addresses spinalstenosis and other ailments of a spine while maintaining mobility of afacet joint, the implant comprising: an anchoring plate having a cavityand a first notch; a facet joint spacer having a pivoting endpositionable within the cavity through the first notch to form anarticulation joint such that the facet joint spacer is pivotablyconnected with the anchoring plate, the facet joint spacer sized andshaped to fit between a superior facet and an inferior facet forming thefacet joint; said anchoring plate having a bore; a bone screw insertablethrough said bore; and said first bore receives and guides the bonescrew into a vertebra to anchor said anchoring plate, wherein when thefacet joint spacer is positioned between the superior facet and theinferior facet a portion of the articulation joint is outside of thefacet joint.
 11. The implant of claim 10, wherein: said bore is a firstbore; and said anchoring plate has a second bore; and further comprisinga locking screw having a locking head and a chisel end, said lockingscrew being insertable through said second bore; said second borereceives the locking screw so that said locking head preventsdisplacement of the bone screw.
 12. The implant of claim 11, wherein thelocking screw is positioned medially relative to the bone screw in apatient.
 13. The implant of claim 11, wherein when said facet jointspacer is movably connected with said anchoring plate said facet jointspacer is adapted to swivel and tilt.
 14. The implant of claim 10,wherein said pivoting end is a ball and said cavity is a socket adaptedto receive the ball.
 15. The implant of claim 10, wherein: saidanchoring plate includes a posterior face and an anterior face; saidposterior face has the first notch; said anterior face has a secondnotch; said pivot end is positionable within said cavity through saidfirst notch.
 16. The implant of claim 15, further comprising a plugadapted to lock the pivot end within the cavity; wherein said plug ismated with said anchoring plate by press fitting said plug within saidfirst notch.
 17. A facet joint implant that addresses spinal stenosisand other ailments of a spine while maintaining mobility of a facetjoint, the implant comprising: an anchoring plate; a facet joint spacersized and shaped to fit between a superior facet and an inferior facetforming the facet joint; wherein one of the anchoring plate and thefacet joint spacer includes a socket, and the other of the anchoringplate and the facet joint spacer includes an end having a ballreceivable within the socket to form a multiple direction articulationjoint, wherein the end having the ball is positionable within the socketvia a notch formed in the one of the anchoring plate and the facet jointspacer having the socket; said anchoring plate having a bore; a bonescrew insertable through said bore; and said first bore receives andguides the bone screw into a vertebra to anchor said anchoring plate,wherein when the facet joint spacer is positioned between the superiorfacet and the inferior facet a portion of the articulation joint isoutside of the facet joint.
 18. The implant of claim 17, wherein: saidbore is a first bore; and said anchoring plate has a second bore; andfurther comprising a locking screw having a locking head and a chiselend, said locking screw being insertable through said second bore; saidsecond bore receives the locking screw so that said locking headprevents displacement of the bone screw.
 19. The implant of claim 18,wherein the locking screw is positioned medially relative to the bonescrew in a patient.
 20. The implant of claim 17, further comprising aplug adapted to lock the end having the ball within the socket by pressfitting the plug within said notch.